Winch Launch Fatality

On Jun 24, 7:00*pm, Don Johnstone wrote:
What is particularly interesting in both the video and the photographs is
the direction the glider is pointing relative to the cable. In the video
the glider can be seen to yaw as the cable tightens and then further yaw
as the it starts to move.
In the photographs it is clear that the glider is pointing to the right of
the direction of the cable AND stangely is pointed in the same direction as
the K13 parked behind it, a co-incidence perhaps. In both cases it would
appear possible that the glider was not lined up with the cable prior to
launch so that as soon as the cable moved yaw was induced. With a CofG
hook the glider will be more unstable about the yaw axis than was the case
with the more forward release on older gliders. Perhaps that might explain
why this appears to be a "new" phenomenon.

Nope, they lined it up at an angle to the wire then all the other
stuff compounded the problem. There are other videos from Lasham with
the gliders improperly staged which show a similar wobbly takeoff. If
the gilder isn't pointing at the winch, the takeoff will be
'interesting'. Unfortunately, some people in the US are showing the
k-13 photo sequence as proof that winches are too dangerous to use.
This actually forced me to add a paragraph in my winch training
syllabus cautioning pilots to aim gliders at the winch - which any kid
launching a balsa glider with a rubber band would understand without
being told.

To be fair, there very well could have been a wind event that we, in a
dustier climate, would call a "dust devil" which couldn't be seen in
lush green England. We would see it coming and stand down until the
thing passed - then launch and go chase it for the lift it marks.

For Christs sake Bill! Lasham is the largest and most professional gliding
club in the UK and we do about 10,000 winch launches per year, 9,999 of
which go without incident. We do know what we are doing. We either point
the glide directly at the main winch, or just slightly upwind of it in a
crosswind to reduce any initial yaw due to weather cocking.

The K13 incident was caused by a gust, and the glider was landed without
damage or injury. A similar wing drop during an aerotow would be
considered quite unremarkable. The correct thing to do is to pull off if a
wing drops during a winch launch.

Derek Copeland

At 03:42 26 June 2009, bildan wrote:
On Jun 24, 7:00=A0pm, Don Johnstone wrote:
What is particularly interesting in both the video and the photographs
is
the direction the glider is pointing relative to the cable. In the
video
the glider can be seen to yaw as the cable tightens and then further
yaw
as the it starts to move.
In the photographs it is clear that the glider is pointing to the
right
o=
f
the direction of the cable AND stangely is pointed in the same
direction
=
as
the K13 parked behind it, a co-incidence perhaps. In both cases it
would
appear possible that the glider was not lined up with the cable prior
to
launch so that as soon as the cable moved yaw was induced. With a CofG
hook the glider will be more unstable about the yaw axis than was the
cas=
e
with the more forward release on older gliders. Perhaps that might
explai=
n
why this appears to be a "new" phenomenon.

Nope, they lined it up at an angle to the wire then all the other
stuff compounded the problem. There are other videos from Lasham with
the gliders improperly staged which show a similar wobbly takeoff. If
the gilder isn't pointing at the winch, the takeoff will be
'interesting'. Unfortunately, some people in the US are showing the
k-13 photo sequence as proof that winches are too dangerous to use.
This actually forced me to add a paragraph in my winch training
syllabus cautioning pilots to aim gliders at the winch - which any kid
launching a balsa glider with a rubber band would understand without
being told.

To be fair, there very well could have been a wind event that we, in a
dustier climate, would call a "dust devil" which couldn't be seen in
lush green England. We would see it coming and stand down until the
thing passed - then launch and go chase it for the lift it marks.

You should not necessarily point the glider at the winch, you should point
it in the direction that the cable is going to take. If there is a bow in
the cable then the glider should not point at the winch but towards the
bow so that yaw is not induced.
Of course the ideal and proper situation is that the cable runs straight
from the winch to the takeoff point when the cable direction and the winch
are both in the same direction.

The correct thing to do if a wing drops is to release the cable, semantics
maybe but can we please get the terminology right at least.

Just to illustrate the point many years a go a gliding site in the UK
winch launched on a dog leg, the winch cable changed direction halfway
down the run by being taken round a telegraph pole and the launch was
always towards the pole. The change in direction when the cable reached
the top of the pole and slipped off was interesting, the good news was
that CofG hooks were not common so the pull of the cable helped to damp
the yaw induced. I would not want to do it in a modern glider with a CofG
hook, damm dangerous I would think.



At 07:30 26 June 2009, Derek Copeland wrote:
For Christs sake Bill! Lasham is the largest and most professional
gliding
club in the UK and we do about 10,000 winch launches per year, 9,999 of
which go without incident. We do know what we are doing. We either point
the glide directly at the main winch, or just slightly upwind of it in a
crosswind to reduce any initial yaw due to weather cocking.

The K13 incident was caused by a gust, and the glider was landed without
damage or injury. A similar wing drop during an aerotow would be
considered quite unremarkable. The correct thing to do is to pull off if
a
wing drops during a winch launch.

Derek Copeland

At 03:42 26 June 2009, bildan wrote:
On Jun 24, 7:00=A0pm, Don Johnstone wrote:
What is particularly interesting in both the video and the
photographs
is
the direction the glider is pointing relative to the cable. In the
video
the glider can be seen to yaw as the cable tightens and then further
yaw
as the it starts to move.
In the photographs it is clear that the glider is pointing to the
right
o=
f
the direction of the cable AND stangely is pointed in the same
direction
=
as
the K13 parked behind it, a co-incidence perhaps. In both cases it
would
appear possible that the glider was not lined up with the cable prior
to
launch so that as soon as the cable moved yaw was induced. With a
CofG
hook the glider will be more unstable about the yaw axis than was the
cas=
e
with the more forward release on older gliders. Perhaps that might
explai=
n
why this appears to be a "new" phenomenon.

Nope, they lined it up at an angle to the wire then all the other
stuff compounded the problem. There are other videos from Lasham with
the gliders improperly staged which show a similar wobbly takeoff. If
the gilder isn't pointing at the winch, the takeoff will be
'interesting'. Unfortunately, some people in the US are showing the
k-13 photo sequence as proof that winches are too dangerous to use.
This actually forced me to add a paragraph in my winch training
syllabus cautioning pilots to aim gliders at the winch - which any kid
launching a balsa glider with a rubber band would understand without
being told.

To be fair, there very well could have been a wind event that we, in a
dustier climate, would call a "dust devil" which couldn't be seen in
lush green England. We would see it coming and stand down until the
thing passed - then launch and go chase it for the lift it marks.

On Jun 26, 10:30*am, Don Johnstone wrote:
You should not necessarily point the glider at the winch, you should point
it in the direction that the cable is going to take. If there is a bow in
the cable then the glider should not point at the winch but towards the
bow so that yaw is not induced.

A typical answer for a steel cable user. Steel digs in to the ground
as it is puled out. You don't know if a steel cable will maintain its
initial direction or 'twang' back to center jerking the glider around.

UHMWPE/Dyneema rope will take a dead straight line from the glider to
the winch as it is tensioned. The stuff is so light that it easily
skips sideways over weeds and grass. If it fails to straighten out,
it's likely caught on something solid and you'd best investigate.

Yet another reason to dump steel cable.

When we did a trial with Plasma (similar to Dyneema) cable on one drum and
steel cable on the other drum of a two drum winch, I can't say that I
noticed any difference between the two in terms of straightening out. The
Plasma cable did give higher launches, by a hundred feet or so, but the
cost is unfortunately rather prohibitive.

It is a good idea to keep the airfield grass as short as possible so that
cables will slide over it and straighten out as they are tensioned. This
also reduces the chances of groundloops or cartwheels if a wing drops.

At my club we pull the cables just past the launch point so there is
enough slack to reach the second glider, normally on the upwind side by
just over half a wingspan. There is therefore a small amount of offset,
but this generally does not cause a problem. The upwind side is preferred
as you launch the downwind cable first, which tends to drift away from the
second cable, reducing the risk of picking it up. Also reduces the chance
of the cables crossing at the winch end during the wind in.

Derek Copeland



At 19:35 26 June 2009, bildan wrote:
On Jun 26, 10:30=A0am, Don Johnstone wrote:
You should not necessarily point the glider at the winch, you should
poin=
t
it in the direction that the cable is going to take. If there is a bow
in
the cable then the glider should not point at the winch but towards
the
bow so that yaw is not induced.

A typical answer for a steel cable user. Steel digs in to the ground
as it is puled out. You don't know if a steel cable will maintain its
initial direction or 'twang' back to center jerking the glider around.

UHMWPE/Dyneema rope will take a dead straight line from the glider to
the winch as it is tensioned. The stuff is so light that it easily
skips sideways over weeds and grass. If it fails to straighten out,
it's likely caught on something solid and you'd best investigate.

Yet another reason to dump steel cable.

On 26 June, 17:30, Don Johnstone wrote:
You should not necessarily point the glider at the winch, you should point
it in the direction that the cable is going to take. If there is a bow in
the cable then the glider should not point at the winch but towards the
bow so that yaw is not induced.
Of course the ideal and proper situation is that the cable runs straight
from the winch to the takeoff point when the cable direction and the winch
are both in the same direction.

The correct thing to do if a wing drops is to release the cable, semantics
maybe but can we please get the terminology right at least.

Just to illustrate the point many years a go a gliding site in the UK
winch launched on a dog leg, the winch cable changed direction halfway
down the run by being taken round a telegraph pole and the launch was
always towards the pole. The change in direction when the cable reached
the top of the pole and slipped off was interesting, the good news was
that CofG hooks were not common so the pull of the cable helped to damp
the yaw induced. I would not want to do it in a modern glider with a CofG
hook, damm dangerous I would think.

Don,

You are clearly referring to the Scottish Gliding Union at Portmoak
airfield where I have been member since 1977. We continued launching
on the dogleg ash strip for many years after that including many
gliders with C of G hooks with no problem at all (including, in my
case over those years, K6E, Diamant, Std Cirrus, Kestrel 19, Nimbus
2C). The point that is is relevant to the "where to point the glider"
issues is this: Waiting for a launch we lined up one behind the other
straight down the strip with the cable coming straight into the
glider. We were therefore pointing well to one side of the winch but
the gliders took off perfectly straight down the strip. I was never
particularly aware of any direction change during the launch.

Now that we launch straight towards the winch on the main grass parts
of the airfield we have more, not less, issues with gliders being
swung by the cable and that is because the gliders queue side by side
with a gap between them for the cable retrieve vehicle to pass
through. For each glider the cable has to be pulled over to the
glider leaving a bow in the last 50m or so of the cable. A steel
cable being pulled through grass by a our lowish power winch does
*not* pull straight as the slack is taken up and can easily swing the
glider right at the start of the ground run. When I launch I always
insist the last 50m of cable is pulled as straight as possible and not
just that the drogue chute is pulled to the front of the glider. If
that were not possible I would agree that the glider should more or
less line up with the closest 50m of cable when launching off grass.
When launching from a hard runway (or our old ash strip) this is much
less of an issue because the cable can slip sideways over the ground
so much more easily.

John Galloway